Using THR for Exercise Intensity

When you exercise, your heart beats faster to meet the demands of your muscles for more blood and oxygen. The more intense the exercise bout, the faster your heart beats. Thus, all factors considered, monitoring your heart rate during exercise provides a very accurate reflection of the metabolic intensity of the exercise. Several techniques can be used to determine an appropriate target heart rate.

Exercise intensity can be prescribed in terms of heart rate (HR) by using specific heart-rate values that are approximately equal to 60 to 80 percent of V02max. One method involves monitoring HR at each stage of a maximal graded exercise test (GXT). Heart rate is plotted on a graph against the V02max (or MET) equivalents of each stage of the test in order to define the slope of heart rate response to exercise (refer to Figure 1). From this relationship, the exercise heart rate associated with a given percent of V02max can be obtained. While this method is generally the most accurate approach for determining an appropriate level of exercise intensity, it is often impractical since it requires a person to complete a maximal GXT — with its associated logistical and safety considerations.

A line of best fit has been drawn through the data points on this plot of heart rate and oxygen consumption data observed during a hypothetical maximal exercise test in which V02max was observed to be 38 ml per kg -1 per min -1 and maximal heart rate was 184 beats per/minute. A target heart rate range was determined by finding the heart rates that correspond to 50 percent and 85 percent of V02max.

For this individual, 50 percent of V02max was approximately 19 ml per kg -1 per min -1 and 85 percent of V02max was approximately 32 ml per kg -1 per min -1. The corresponding heart rates are approximately 130 and 168 beats/minute. The target heart rate range for this individual is 130 to 168 beats/minute.

Another method for assessing exercise intensity is based on the observation that 70 and 85 percent of maximal heart rate is equal to approximately 60 and 80 percent of functional capacity (V02max). For example: